1. Field of the Invention
The invention pertains to the art of limiting glass-ceramic cooking platform temperatures through limiting the wattage supplied to the heater associated with the platform.
2. Description of the Prior Art
U.S. Pat. No. 3,798,416 discloses a temperature control system stated to provide relatively economical temperature control using solid-state components and which is stated to be especially suitable for use with the electrically heated glass-ceramic cook-tops and providing temperature limiting of both the electric heating element and the cook-top. This patent also refers to prior art temperature control systems of other than the solid-state type. This patent is mentioned mainly because it shows one arrangement for obtaining temperature control for a glass cook-top but in a form considered to be relatively expensive as compared to my arrangement.
U.S. Pat. No. 3,005,896 discloses an arrangement for temperature control of a cooking vessel in which a positive temperature coefficient of resistance sensor is associated with a heater for a bimetal to obtain the control. While the arrangement there shown has superficial similarities to my invention, it differs in a number of ways including being a full range temperature control as distinguished from a wattage limiting control which is capable only of limiting the rate of input to the heater element in a direction to limit the temperature of a glass cook-top. Because the last noted patent arrangement is for the purpose of obtaining full range temperature control, it is substantially more complicated than an arrangement according to my invention. Finally, and most importantly, the patented arrangement would not be capable of functioning as a temperature limiting control for a cooking platform since its temperature range as disclosed is coupled to the temperature range of the cooking vessel, which is very substantially less than the temperature which the glass-ceramic cooking platform will achieve in normal operation. Thus a typical nickel or nickel alloy of the type used as the sensor in such an application has a temperature coefficient of resistance which changes from positive to negative in a range between about 900.degree.F. and 1100.degree.F (482.degree.C and 593.degree.C). Such a temperature sensor would cause a runaway if applied to limit a glass platform temperature since the glass platform temperature will at times, be in the neighborhood of 1300.degree.F (704.degree.C) or higher.